linux-kernel - Re: [PATCH v6 8/8] ima: add FIRMWARE_PARTIAL

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Date:   Fri, 5 Jun 2020 16:31:14 -0700
From:   Scott Branden <scott.branden@...adcom.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Brown <david.brown@...aro.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>, bjorn.andersson@...aro.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Olof Johansson <olof@...om.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Colin Ian King <colin.king@...onical.com>,
        Kees Cook <keescook@...omium.org>,
        Takashi Iwai <tiwai@...e.de>, linux-kselftest@...r.kernel.org,
        Andy Gross <agross@...nel.org>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v6 8/8] ima: add FIRMWARE_PARTIAL_READ support

Hi Mimi,

On 2020-06-05 4:19 p.m., Mimi Zohar wrote:
> Hi Scott,
>
> On Fri, 2020-06-05 at 15:59 -0700, Scott Branden wrote:
>> @@ -648,6 +667,9 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>>   	enum ima_hooks func;
>>   	u32 secid;
>>   
>> +	if (!file && read_id == READING_FIRMWARE_PARTIAL_READ)
>> +		return 0;
> The file should be measured on the pre security hook, not here on the
> post security hook.  Here, whether "file" is defined or not, is
> irrelevant.  The test should just check "read_id".
OK, will remove the !file from here.
>
> Have you tested measuring the firmware by booting a system with
> "ima_policy=tcb" specified on the boot command line and compared the
> measurement entry in the IMA measurement list with the file hash (eg.
> sha1sum, sha256sum)?
Yes, I enabled IMA in my kernel and added ima_policy=tsb to the boot 
command line,

Here are the entries from 
/sys/kernel/security/ima/ascii_runtime_measurements of the files I am 
accessing.
Please let me know if I am doing anything incorrectly.

10 4612bce355b2dbc45ecd95e17001636be8832c7f ima-ng 
sha1:fddd9a28c2b15acf3b0fc9ec0cf187cb2153d7f2 
/lib/firmware/vk-boot1-bcm958401m2.ecdsa.bin
10 4c0eb0fc30eb7ac3a30a27f05c1d2a8d28d6a9ec ima-ng 
sha1:b16d343dd63352d10309690c71b110762a9444c3 
/lib/firmware/vk-boot2-bcm958401m2_a72.ecdsn

The sha1 sum matches:
root@...ericx86-64:/sys/kernel/security/ima# sha1sum 
/lib/firmware/vk-boot1-bcm958401m2.ecdsa.bin
fddd9a28c2b15acf3b0fc9ec0cf187cb2153d7f2 
/lib/firmware/vk-boot1-bcm958401m2.ecdsa.bin

root@...ericx86-64:/sys/kernel/security/ima# sha1sum 
/lib/firmware/vk-boot2-bcm958401m2_a72.ecdsa.bin
b16d343dd63352d10309690c71b110762a9444c3 
/lib/firmware/vk-boot2-bcm958401m2_a72.ecdsa.bin


>
> Mimi
>
>> +
>>   	if (!file && read_id == READING_FIRMWARE) {
>>   		if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
>>   		    (ima_appraise & IMA_APPRAISE_ENFORCE)) {